Effect of thermal oxidation parameters on photo-electrochemical performance of hematite photoanodes

Hematite thin films were fabricated by the thermal oxidation of electrodeposited Fe layers on fluorine-doped tin oxide substrates. The effects of oxidation atmosphere (air, argon, and nitrogen), temperature (350–650 °C), and duration on the photo-electrochemical performance were systematically investigated. Linear sweep voltammetry, Mott-Schottky analysis, and electrochemical impedance spectroscopy were used to evaluate the photo-electrochemical response. The photocurrent density increased with oxidation time, reached a maximum, and then declined upon further exposure. The highest photocurrent density (0.56 mA cm −2 at 1.6 V RHE ) was achieved by annealing in argon at 450 °C for 96 h. The optical band gap remained nearly constant (∼2.0 eV) under all conditions, indicating that changes in photo-electrochemical activity mainly originated from electronic and structural modifications rather than changes in optical absorption. This work focuses on compact, undoped hematite films and deliberately avoids additional performance-enhancing strategies, such as doping, co-catalysts, and nanostructuring, in order to isolate the sole contribution of oxidation parameters. These findings demonstrate that careful control of oxidation conditions provides a simple, cost-effective, and scalable approach for improving hematite photoanodes for solar water splitting.